Combustor liner and method for making thereof

ABSTRACT

A combustor liner is provided having first and second annular bands which define an overlapping circumferential joint area, wherein a weld is disposed in the joint area encompassing substantially all of the axial length of the joint area. A method for producing such a combustor liner is also provided.

[0001] This invention relates generally to combustor liners for gasturbine engines and more particularly to liners which are assembled froma plurality of annular bands.

[0002] A gas turbine engine includes a compressor that providespressurized air to a combustor wherein the air is mixed with fuel andignited for generating hot combustion gases. These gases flow downstreamto one or more turbines that extract energy therefrom to power thecompressor and provide useful work such as powering an aircraft inflight. Combustors used in aircraft engines typically include inner andouter combustor liners to protect the combustor case and surroundingengine components from the intense heat generated by the combustionprocess.

[0003] One particular type of combustor liner is comprised of aplurality of annular sheet metal bands that are joined together atoverlapping circumferential joints to form an assembled liner. Prior artinner and outer liners of this type are presently constructed by brazingthe sheet metal bands together at the overlapping joints. The processinvolves tack welding the bands in place, followed by manually applyinga braze filler at each braze joint, followed by a furnace cycle brazeoperation. The braze joints are then inspected, for example by x-rayingthe joints. A large proportion of liners joined in this manner, in someinstances over 90%, exhibit defects such as voids in the braze joints,which require a second braze operation involving the application of moreslurry in the areas which have braze voids and a subsequent secondfurnace cycle and additional x-ray inspection. Brazing of the liners iscostly and increases the manufacturing cycle time needed to produce theliners.

[0004] Accordingly, there is a need for combustor liners having a lowercost and simplified manufacturing process.

BRIEF SUMMARY OF THE INVENTION

[0005] The above-mentioned need is met by the present invention, whichprovides a combustor liner having first and second annular bands whichhave an overlapping circumferential joint area. A weld is disposed inthe joint area and encompasses substantially all of the axial length ofthe joint area. The invention also provides a method for producing sucha combustor liner.

[0006] The present invention and its advantages over the prior art willbecome apparent upon reading the following detailed description and theappended claims with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The subject matter that is regarded as the invention isparticularly pointed out and distinctly claimed in the concluding partof the specification. The invention, however, may be best understood byreference to the following description taken in conjunction with theaccompanying drawing figures in which:

[0008]FIG. 1 is a cross-sectional view of a combustor assembly.

[0009]FIG. 2 is an enlarged cross-sectional view of a prior artcombustor liner band joint.

[0010]FIG. 3 is an enlarged cross-sectional view of a combustor linerband joint constructed in accordance with the present invention.

[0011]FIG. 4 is an enlarged view of a portion of FIG. 3 showing the bandjoint in more detail.

[0012]FIG. 5 is a side view of an exemplary laser welding apparatus anda representative combustor liner positioned therein.

DETAILED DESCRIPTION OF THE INVENTION

[0013] Referring to the drawings wherein identical reference numeralsdenote the same elements throughout the various views, FIG. 1illustrates an exemplary combustor 10. The illustrated combustor 10 isof annular design which has a central axis 11 (shown in FIG. 5)coincident with the longitudinal axis of a gas turbine engine (notshown) when assembled, although the present invention is equallyapplicable to other types of combustors having liners disposed about anaxis. The combustor 10 has circumferentially extending outer and innerliners 12 and 14, which define an annular combustion chamber 15. theliners 12 and 14 are connected at their forward ends by an annular domeassembly 16. Each liner has a mounting flange 18 attached to its aftend. Film cooling of the liners 12 and 14 is provided by a plurality ofcooling slots 25, which are described in more detail below.

[0014] Referring now to FIG. 2, an inner liner 14 constructed inaccordance with the prior art is illustrated. It should be noted thatthe following descriptions are equally applicable to an outer liner 12.The inner liner 14 is built up from a plurality of bands 20, each ofwhich has a forward end 22 and an aft end 24. The bands are typicallyformed of a high-temperature oxidation resistant alloy such as HASTELLOYalloy X. Each band 20 is connected to the axially adjacent bands 20 by abrazed-joint 27. The bands 20 have a ridge 26 formed therein whichcontains a plurality of cooling holes 28. When the inner liner 14 isassembled, the ridges 26 and the aft end 24 of the adjacent band 20cooperate to form a cooling slot 25. A braze joint area 30 extendsaround the circumference of the band 20 and is delimited in the axialdirection by the overlap of the adjacent bands 20. The portion of theband 20 extending past ridge 26 has an axial length L1 that is equal tothe axial length of the joint area 30, which in the illustratedembodiment is about 2.54 cm (1 in.). The prior art inner liner 14 istypically constructed by brazing the sheet metal bands 20 together.Initially, the bands 20 are temporarily held together by a plurality oftack welds (not shown). Then a slurry of a suitable braze material 32 isapplied to the joint areas 30. The inner liner 14 is then placed in afurnace and subjected to a braze operation, which involves heating theinner liner 14 to a temperature above the melting point of the brazematerial 32 but below that of the band 20 this causes the braze materialto melt and flow in the braze joint area 30. Upon cooling the brazematerial solidifies, joining bands 20 to each other. Unfortunately, thebrazing process is not perfect, causing some of the joints 27 to havevoids wherein no braze material is present. This is unacceptable forstructural and heat transfer reasons. Therefore, after the braze cycleis complete the joints 27 are inspected for defects, for example byx-raying the joints 27. A large proportion of the inner liners 14, insome instances over 90%, require a second braze operation which involvesthe application of more slurry in the areas which have braze voids and asubsequent second furnace braze cycle. This rework of the inner liners14 is costly and increases the production cycle time needed tomanufacture the inner liners 14.

[0015]FIGS. 3 and 4 illustrate a combustor liner 114 constructed inaccordance with the present invention. It should be noted that, exceptfor the details of the joints described below, and the method ofassembling the joints, the inner liner 114 is generally identical to theprior art inner liner 14 described above. Although the illustration isof an inner liner 114 the invention is equally applicable to outerliners as well. The inner liner 114 is built up from a plurality ofbands 116, each of which has a forward end 118 and an aft end 120. Thebands 116 have a ridge 122 formed therein which contains a plurality ofcooling holes 124. When the liner is assembled, the ridges 122 cooperatewith the aft end 120 of the adjacent band 116 to form a cooling slot125. A weld joint area 126 extends around the circumference of the band116 and is delimited in the axial direction by the overlapping areas ofthe adjacent bands 116. The band 116 has a flange 117 extending forwardpast ridge 122. A portion of the flange 117 is relatively flat as viewedin cross-section. This flat portion has a an axial length L2 that issubstantially equal to the axial length of the weld joint area 126. Inthe exemplary embodiment the axial length L2 is about 40% of the axiallength L1 of the braze joint 27 described above. A weld 127 comprisingfirst and second weld beads 128 and 130 is disposed in the weld jointarea 126. The weld beads 128 and 130 penetrate through both bands 116 atthe weld joint area 126 the weld beads 128, 130 at least partiallyoverlap each other in the axial direction, for example by about 10% ofthe weld bead diameter D (see FIG. 4). The weld bead diameter D and theaxial length L2 of the flange 117 are chosen so that substantially allof the length L2 will be encompassed by the weld beads 128, 130. Thisprevents having voids within the weld joint area 126 and ensures thatthe surface areas of the bands 116 that are within the weld joint area126 will be in uninterrupted contact, ensuring sufficient heat transferfrom one band 116 to the other.

[0016] The axial length L2 of the weld joint area 126 may be madeshorter than the brazed joint area axial length L1 because of thegreater strength of the welded joint as compared to the brazed joint.The axial length L2 may of course be varied to suit a particularapplication. If the axial length L2 is too short the joint between thebands will not be able to sustain the expected shear loads duringoperation. On the other hand, excessive axial length requires additionalprocessing and materials without providing an additional benefit. In theillustrated example the weld joint area axial length L2 is about 3 to 5times the total thickness T of both bands 116 at the weld joint area126.

[0017] The bands 116 are joined by a laser welding process. The laserwelding process is especially suited to joining the bands 116, whichhave a thickness of only about 1.0 mm (0.04 in.) each. The laser weldingprocess, unlike other welding processes, allows the bands 116 to bejoined without overheating them or distorting them into an out-of-roundcondition. Initially, the bands 116 are temporarily held together by aplurality of tack welds in an known manner. Referring to FIG. 5, Thestacked, tack welded bands 116 are then placed in a vertical position ona rotary table 150 having a rotating mechanism 152. The inner liner 114is rotated at a predetermined speed. The rotation speed is chosen basedon the part radius to give the desired linear weld speed, which isrelated to the other weld parameters described below. A laser apparatus158 of a known type capable of generating and directing a laser beam,for example a Nd:YAG or CO₂ laser, is suspended from a support column154 by a moveable carriage 156, and may be traversed along an axisparallel to the combustor's axis 11 as shown by arrow Y. The inner liner114, rotary table 150, and the laser apparatus 158 may be placed in aninert gas atmosphere to prevent contamination of the weld joints. Thelaser apparatus 158 is aligned with the axial position of the firstjoint and the laser beam is energized. As the beam strikes the surface,it melts the band 116 in the area where it impinges, creating a firstweld bead 128 which penetrates both bands 116, joining the bands 116together as the inner liner 114 rotates.

[0018] The laser weld parameters are chosen to result in the fullpenetration weld described above. Suitable examples of weld parameterswould include a Nd:YAG laser of about 500 to about 3000 Watts outputpower, operated continuously, with a weld speed of about 5 to about 1500inches per minute, or an Nd:YAG laser pulsed at about 10 to about 60Joules/pulse with a weld speed of about 3 to about 30 inches per minute.A CO₂ laser of about 1000 to about 5000 Watts output power could also beused, operated continuously, with a weld speed of about 50 to about 500inches per minute. These parameters are intended as examples and may bevaried to suit a particular application. Any type of laser weldequipment and parameters operable to produce full penetration welds maybe used.

[0019] After the first weld bead 128 is created around the entirecircumference of the weld joint area 126, the laser beam is de-energizedand the laser apparatus 158 is then moved a small distance along the Yaxis. The beam is again directed at the weld joint area 126 while theinner liner 114 is rotated. This forms a second weld bead 130 whichpenetrates both bands 116 in the joint area 126 and also overlaps thefirst weld bead 128 in the axial direction, as shown in FIG. 4. Togetherthe overall axial length of the first and second weld beads 128 and 130encompasses substantially all of the weld joint length L2. Aftercompleting a first joint, the laser beam directing apparatus 158 maythen be indexed along the Y axis to the next joint and the weldingprocess repeated until the entire inner liner 114 has been laser welded.When all of the joints are completed they are inspected in aconventional manner, for example by X-ray inspection.

[0020] The invention described herein provides an improved combustorliner and method for its assembly. The process described herein will bemuch less labor intensive relative to brazing of liners since the brazeslurry application is eliminated, there is no furnace cycle timerequired and no second braze operation. The end result is a significantreduction in cost and cycle time to complete the liner joining process.

[0021] The foregoing has described a combustor liner having first andsecond annular bands which define an overlapping circumferential jointarea, wherein a weld is disposed in the joint area encompassingsubstantially all of the axial length of the joint area; and a methodfor producing such a combustor liner. While specific embodiments of thepresent invention have been described, it will be apparent to thoseskilled in the art that various modifications thereto can be madewithout departing from the spirit and scope of the invention as definedin the appended claims.

What is claimed is:
 1. A combustor liner comprising: a first annularband having forward and aft ends, said first annular band disposed abouta central axis; a second annular band having forward and aft ends, saidsecond. annular band disposed about said central axis and having aflange disposed in an overlapping relationship with said first annularband so as to define a circumferentially extending joint area; a welddisposed in said joint area comprising a first circumferentiallyextending weld bead penetrating said first and second annular bands, anda second circumferentially extending weld bead penetrating said firstand second annular bands and disposed adjacent to said firstcircumferentially extending weld bead, wherein at least a portion ofsaid first and second weld beads overlap each other.
 2. The combustorliner of claim 1 wherein said flange of said second annular band has afirst length in an axial direction, and said weld has a second length inan axial direction, said second length being substantially equal to saidfirst length.
 3. The combustor liner of claim 1 further comprisingadditional annular bands disposed about said central axis, each of saidadditional annular bands being disposed in overlapping relationship withan adjacent annular band so as to create an additional circumferentiallyextending joint area, wherein a weld is disposed in each of saidadditional joint areas, each of said welds comprising first and secondoverlapping weld beads.
 4. A combustor liner comprising: a first annularband having forward and aft ends, said first annular band disposed aboutan axis; a second annular band having forward and aft ends, said secondannular band disposed about said axis and having a flange disposed in anoverlapping relationship with said first annular band so as to define acircumferentially extending joint area; a weld disposed in said jointarea comprising a circumferentially extending weld bead penetrating saidfirst and second annular bands, wherein said forward section of saidsecond annular band has a first length in an axial direction, and saidweld has a second length in an axial direction, said second length beingsubstantially equal to said first length.
 5. The combustor liner ofclaim 4 further comprising additional annular bands disposed about saidaxis, each of said additional annular bands being disposed inoverlapping relationship with an adjacent annular band so as to createan additional circumferentially extending joint area, wherein a weld isdisposed in each of said additional joint areas, each of said weldscomprising first and second overlapping weld beads
 6. A method ofassembling a combustor liner, comprising: providing a plurality ofannular bands disposed about a central axis, each of said bands having aforward and an aft end; positioning first and second ones of saidannular bands in an overlapping relationship relative to each other, soas to define a circumferentially extending joint area; directing a laserbeam at said joint area at a first axial position and concurrentlyrotating said first and second annular bands about said central axis soas to expose the entire circumference of said joint area to said laserbeam, whereby a first weld bead is formed; and directing said laser beamat said joint area at a second axial position while rotating said firstand second annular bands about said central axis so as to expose theentire circumference of said first joint area to said laser beam,whereby a second weld bead is formed, said second bead at leastpartially overlapping said first weld bead.
 7. The method of assemblinga combustor liner of claim 6 wherein each of said annular bands includesa flange having a first length in an axial direction, and first andsecond weld beads have an overall length in an axial direction, saidoverall length being substantially equal to said first length.
 8. Themethod of assembling a combustor liner of claim 6 further comprising:disposing additional ones of said annular bands in an overlappingrelationship with an adjacent one of said annular bands so as to createan additional circumferentially extending joint area, and; directing alaser beam at said additional joint area at a first axial position andconcurrently rotating said additional ones of said annular bands aboutsaid central axis so as to expose the entire circumference of saidadditional joint area to said laser beam, whereby a third weld bead isformed; and directing said laser beam at said additional joint area at asecond axial position while rotating said additional annular bands aboutsaid central axis so as to expose the entire circumference of saidadditional joint area to said laser beam, whereby a fourth weld bead isformed, said fourth bead at least partially overlapping said third weldbead